Strong musty smell from my washin machine top-loader?

We have a strong musty/stale smell coming from our Simpson Esprit 450 top-loading washing machine. It works fine, and the clothes come out smelling and looking fine, but the machine itself exudes a nasty stale smell.

Tried researching on the net, calling the manufacturer (it is no longer under warranttee but they made suggestions), and calling a repairman. Tried washing with epsom salt, and also a descaler. Nothing has worked. Even tried taking apart the top parts, but am stuck at the bowl. If I move it around I can hear a liquid stuck in it, below, but can't take off any more pieces to investigate.

Some websites claim that certain liquid detergents leave behind deposits of gunk that fungus and such can grow in, and the only solution is to take apart the washer and clean this out.

Any suggestions?